Modern hair dyeing methodology has developed from its initiation in the 1950s to the point where today it is the third largest product type in the hair care category, following shampoos and conditioners.
One widely employed method for dyeing hair is based upon the production of the natural pigment melanin. The exact structure of melanin it not known. It is a polymer produced from tyrosine by a series of metabolic reactions the exact course of which remains to be clarified. To take advantage of what has been elucidated with respect to the formation of melanin, it has become the practice of the art to utilize 5,6-dihydroxyindole (DHI) or 5,6-dihydroxyindole-2-carboxylic (DHICA) as the dyeing agent. These compounds have been clearly established as intermediates in the pathway leading to the production of melanin.
There are a number of problems associated with the use of DHI. It is difficult and expensive to synthesize and is extremely unstable in air. It rapidly decomposes in air to form other materials which are ineffective as hair colorants.
Diacetoxyindole (DAI) is used by the art in its attempts to avoid these problems with DHI. The practice has been to package DAI under mildly alkaline conditions in packages designed to protect the ingredients from air. Over the course of the time, between the initial packaging and the final use, the DAI is hydrolyzed to DHI. Since it is protected from air by the packaging, the DHI remains stable until it is ready for use.
It is known that use of DHI alone requires a long dyeout time. Therefore a variety of accelerators has been employed to hasten the dye formation. Oxidants, such as hydrogen peroxide, are the most widely employed of the various accelerators which have been proposed.
The use of oxidants has not been particularly successful with DHI, because oxidation takes place before the DHI penetrates the hair. Ideally, the DHI should penetrate the hair before oxidation takes place so that the pigment forms within the hair fiber. When the colorant forms in this manner, the color does not easily wash out. In contrast, if oxidation and melanin formation take place in the solution there is little or no dyeing effect. If oxidation takes place on the surface of the hair, the coloring is easily washed away during shampooing.
In attempts to avoid these problems, the art has adopted a two step process. DHI is applied first and allowed to penetrate into the hair. The oxidant is applied in a second step. This procedure is described, for example, in U.S. Pat. No. 2,934,396. Such procedures are lengthy and inconvenient.
It is one object of this invention to provide a one-step dyeing procedure, that is, a method, in which DHI and oxidant are applied to the hair simultaneously.
Dyeing with DHI is very attractive to many consumers, since its conversion to melanin is close to the natural pigmentation process. However, there are disadvantages. One such disadvantage is that, while natural hair color comes in an inexhaustible variety of shades, many oxidants which are used in combination with DHI dye the hair only to a gray or black color with little or no warmth. Extensive research efforts have been undertaken to find ways to modify the final color result after dyeing with DHI.
One way to obtain a brown tonality is through use of hydrogen peroxide. In this procedure, the hair is first dyed black through formation of melanin and then partially bleached to brown through destruction of part of the melanin. A clear disadvantage is the waste of DHI, which is supplied at the beginning. This is important, because DHI is an expensive raw material, and will control the price of the final product.
A second disadvantage is the fact that uneven and unpredictable results are often obtained due to the heterogeneity of living hair and the difference in its affinities for the dye, which vary from one person to another.
A third disadvantage is the likelihood of oxidative damage to the keratin of the hair as a result of the use of a product, containing peroxide--noticeable in a coarse feel of the hair. Moreover, hydrogen peroxide is normally used under alkaline conditions, with ammonia or an amine as the alkaline reagent. These alkaline reagents impart strong odors to the hair dyeing compositions and are unacceptable to many users.
A fourth disadvantage is that peroxide attacks and partly destroys the natural hair pigment. This weakens the hair and changes its feel and appearance.
For these reasons, many efforts have been undertaken in the art to avoid the problems connected with the use of hydrogen peroxide.
It is, therefore, another object of the invention to provide a method to dye hair to a dark brown shade without using hydrogen peroxide.